Build Strings with {栂

Unix Power Tools
Build Strings with {栂

by Jerry Peek
01/27/2000

I've been finding more and more uses for the {} pattern-expansion characters in csh, tcsh, and bash. They're similar to *, ?, and [], but they don't match filenames the way that *, ?, and [] do. You can give them arbitrary text (not just filenames) to expand. That "expand-anything" ability is what makes them so useful.

Here are some examples to get you thinking:

To fix a typo in a filename (change fixbold5.c to fixbold6.c):
```
% mv fixbold{5,6}.c
```
An easy way to see what the shell does with {} is by adding echo before the mv:
```
% echo mv fixbold{5,6}.c
mv fixbold5.c fixbold6.c
```
To copy filename to filename.bak in one easy step:
```
% cp filename{,.bak}
```

To print files from other directory(s) without retyping the whole pathname:

% lpr /usr3/hannah/training/{ed,vi,mail}/lab.{ms,out}

That would give lpr all of these files:

/usr3/hannah/training/ed/lab.ms
/usr3/hannah/training/ed/lab.out
/usr3/hannah/training/vi/lab.ms
/usr3/hannah/training/vi/lab.out
/usr3/hannah/training/mail/lab.ms
/usr3/hannah/training/mail/lab.out

...in one fell swoop!

To edit ten new files that don't exist yet:
```
% vi /usr/foo/file{a,b,c,d,e,f,g,h,i,j}
```
That would make /usr/foo/filea, /usr/foo/fileb, ... /usr/foo/filej. Because the files don't exist before the command starts, the wildcard vi /usr/foo/file[a-j] would not work.
An easy way to step through three-digit numbers 000, 001, ..., 009, 010, 011, ..., 099, 100, 101, ... 299 is:
```
foreach n ({0,1,2}{0,1,2,3,4,5,6,7,8,9}{0,1,2,3,4,5,6,7,8,9})
   ...Do whatever with the number $n...
end
```
Yes, csh also has built-in arithmetic, but its @ operator can't make numbers with leading zeros. This nice trick shows that the {} operators are good for more than just filenames.

To create sets of subdirectories:

% mkdir man
% mkdir man/{man,cat}{1,2,3,4,5,6,7,8}
% ls -F man
cat1/  cat3/  cat5/  cat7/  man1/  man3/  man5/  man7/
cat2/  cat4/  cat6/  cat8/  man2/  man4/  man6/  man8/

To print ten copies of the file project_report (if your lpr command doesn't have a -#10 option):
```
% lpr project_repor{t,t,t,t,t,t,t,t,t,t}
```